15 Gallon Tank How much water to replace?

[Georgie Girl]

I'm setting up* a Fluval 15 gal bowfront aquarium. I'm not a noob at this, but I don't know the answer to this: I want to know how much water to replace during a water change. Do you know?

Thanks!

* I've said I'm setting it up for about 18 mos now. Just haven't done it yet. This weekend is the time!

 

[kansas]

Once its set up and cycled, change 50% a week.

 

[ChrissFishes01]

50% may be a good place to start with, but depending on your stocking, you may not need to do that much, especially if you're planting the tank.

Typically, the less we touch the tank the better off they are as long as we're maintaining decent water quality. So if you're only keeping a betta or a small school of White Clouds or something light like that and you have some fast-growing plants, it may be fine to do a couple 25% changes a month. All depends on how the water tests and whether or not you're seeing any visible issues (algae, health issues, etc.).

 

[Azedenkae]

Generally I replace between 20 to 100% of the water. With my current ten gal I replace about 20% every two months or so.

However, it is a planted tank, so there's that.

 

[kansas]

You'll get a lot if different answers to this question.

It's a lot easier to kill a fish with too few water changes than with too many.

 

[Flyfisha]

You need to remove and replace enough each week to keep the nitrates at a safe level.

We are also replacing minerals that fish use to grow.
We remove the hormones fish produce.

My suggestion is to remove exactly the same amount for 6 weeks. By which time you can establish what the nitrates are just before water changes. Nitrates should be ( IMO ) between 20ppm -40 ppm but no more just before water change day.

Clearly there are no hard and fast answers to this question. With a very heavily stocked tank full of dozens of fast growing juvenile fry it’s completely safe to change 40% of the water every couple of days. At least that has worked for me and my fish.

With a single betta I still change 45% every week.
This is my minimum amount.

I changed another 20% of the water on this guy in his 8 gallon yesterday on top of his weekly fresh water supply and I have not received a written complaint.

 

[KingOscar]

It really depends on stocking levels.

All my tanks are lightly stocked and I presently gravel vac and perform a 30-40% water change every 2 weeks. My nitrates never exceed 10-20ppm and that's with zero live plants. I could go even longer and I'm certain my fish would be fine. In fact, that's what I sometimes did in the past... Months between water changes and the fish were fine. But the tanks didn't look as nice due to algae and waste build up as they do now.

If I had to do water changes every week there's no way I'd have 4 tanks running. That's more work than I'm signing up for.

 

[Dunk2]

Generally I replace between 20 to 100% of the water. With my current ten gal I replace about 20% every two months or so.

However, it is a planted tank, so there's that.

As I assume you know, changing water “every two months or so” can lead to disaster for many fish keepers, including those with planted tanks.

If you’re going to continue to mention your water change practices in your posts, I’d suggest that the responsible thing to do would be to explain how you pull it off and that it could lead to disaster in many cases, especially for new fish keepers.

 

[kansas]

You'll know you're not changing enough water when your animals start to get sick and die.

When I was young, I drove drunk a number of times without killing anyone, but I don't recommend it.